With the advent of chemical insecticides in the 1950s, easy control of insect pests appeared to be at hand. However, it soon became obvious that there were significant problems associated with the use of insecticides. Through several decades of use over 500 different arthropodal pests have become resistant to insecticides. This has occurred in addition to the advent of widespread environmental and health hazards associated with the massive use of pesticidal compounds. In addition, many non-target organisms have been adversely affected, and pest resurgence has often occurred because broad-spectrum insecticides have eliminated the natural enemies that had originally helped to keep pest populations in check. To date, however, the protection of agriculturally valuable food and fiber crops from insect, mite, disease, weed, and vertebrate pests in conventional agricultural systems, and the home garden, remains primarily reliant on the continued use and commercial availability of chemical pesticides. For the reasons indicated above, continued reliance solely on conventional pesticides is a questionable strategy for the long-term sustainability of agricultural production. Therefore, alternative strategies for the protection of agriculturally or aesthetically valuable plants are needed.
Current alternatives to conventional pesticides include the strategies promoted by Integrated Pest Management (IPM) programs. These IPM programs advocate the development of biological, cultural, physical and mechanical controls, engineered and inherent host plant resistance, as well as the use of naturally occurring aversive compounds to replace and/or complement the use of pesticidal compounds. This is done with an eye toward enhancing the sustainability of agricultural production. Much of the emphasis in these programs has been placed on the development of biological and cultural control elements, primarily because of increasing resistance by pests to pesticide controls.
However, interest in and development of physical and mechanical barriers and repellents has lagged. Physical controls include the use of heat, sound, light, and radiation to kill pests. Mechanical control is the "reduction of insect populations by means of devices that affect them directly or that alter their physical environment radically" (Pfadt 1978). Mechanical control techniques include the use of handpicking, traps, screens, barriers, sticking agents, and sticky bands.
While some of these techniques are laborious and therefore economically unsuitable for situations other than home gardens, the use of physical barriers can be easily mechanized and made suitable for large-scale farming, as well as the home garden. The concept of using barriers to prevent insect pests from reaching crops is not new. Row covers and reflective mulches have been used extensively to prevent insects from locating crops, either through visual disorientation or acting as simple barriers, as well as for horticultural purposes (Burbutis, P. P., and Lesiwicz, D. S., 1973; Chalfant et al., 1977; Schalk et al., 1979; Wells and Loy 1985; Perring et al., 1989; and Conway et al., 1989). Recently, the use of "trenches" for the trapping of Colorado potato beetles has been shown to be very effective (Moyer 1993). This simple, environmentally sensitive, and exceptionally cost-effective method of controlling Spring and Fall dispersing adult potato beetles has tremendous potential to reduce the need for insecticide use against these pests.
Mechanical barriers such as netting have long been recognized as the most effective method for reducing bird damage to agricultural products such as fruit and vegetable crops (Himelrick, 1985). However, the high cost of materials and difficulty of applying and removing netting have limited the use of this type of barrier to small-scale gardens or research plots. While Fuller-Perrine and Tobin (1992) have developed a cost-effective method for applying netting to trellised vineyards, no practical netting techniques exist for the protection of fruit or vegetable crops on a commercial scale.
Many crops, including cherries, blueberries, strawberries, and sweet corn are plagued by bird pests. Birds are major pests of sweet corn production because they feed extensively on the ear tips, making the entire ear unmarketable. Most barriers investigated to date have been of a solid design (i.e., sheets of woven material, plastic mulches, wire cages, bud caps, etc.), but as described below, it is not necessary to have a solid barrier to prevent pests from reaching the crop or portion of the crop plant to be protected. There are also drawbacks to solid barriers in some situations because they block sunlight penetration, pollination, and water movement necessary for appropriate plant development. In addition, disposal problems could arise. Thus, non-woven barriers, which allow sunlight penetration and pollination, are to be preferred because they have significant pest control capability without adversely affecting plant growth.
In addition, fiber barriers can be constructed in different biodegradable forms that can include: various stable sugar formulas, proteins, cellulose constructs, polyvinyl alcohol, and biodegradable polymers. Dependent upon the substrate and term of protection needed, different barriers, or barriers composed of different compounds, can be constructed. Thus, a short-lived (i.e. 3 weeks before it starts to degrade and/or become ineffectual) barrier may be manufactured for sweet corn that will actually degrade by harvest, thus protecting the ear of corn during the silking period, but disappearing by harvest. Other more long-lasting barriers (6+weeks) may be used around the base of plants (e.g. especially agriculturally valuable crop plants, referred to in this application as "agricultural products") to prevent egg laying (e.g. oviposition) by adult pests such as cabbage maggots. Such barriers will have considerably more stability than conventional foliage applied insecticides which have activity of normally &lt;5 days. Also of substantial benefit is the fact that since these fibers will be made of naturally derived compounds, their breakdown products will be environmentally benign or even beneficial dependent upon the chemical composition of the breakdown product of the applied fibers.
The use of obstructive non-woven fiber barriers to obscure and/or protect plants from pest induced damage is feasible, but may initially be more expensive than insecticide applications in the agribusiness or home garden setting. However, as technology improves and the market becomes wider, cost will decrease to the point of economic feasibility on both the commercial and individual consumer scales. Physical barriers may fill voids in situations where no insecticides are available or where the use of a conventional insecticide is not a viable option. It is also likely that the use of obstructive fiber barriers will find a niche as a new tool in the arsenal of weapons that farmers or home gardeners use to stop or inhibit agricultural pests. That is, obstructive fiber barriers may also be used in combination (e.g. fibers applied in conjunction with common pesticides) with other measures to prevent damage to agricultural produce. The fibers themselves may also be used as a platform for maintaining the activity of a given pesticide compound, sensory repellent, or even biological control element such as Bacillus thuringenesis, on or near a plant far longer than would otherwise be possible. This possibility would reduce the overall use of insecticides on agricultural produce while enhancing their effectiveness.
Another positive feature of the use of fibers themselves in pest prevention is that the use of fiber barriers does not require registration like insecticides, so use could not be delayed by an extensive regulatory process. In addition to being a physical barrier to birds and insects, fibers made from polysaccharides may themselves act as repellents because some bird species have difficulty digesting sucrose (Martinez del Rio 1990; Clark and Mason 1993). Frugivorous birds such as starlings, Sturnus vulgaris, and American robins (Turdus migratorius) lack the digestive enzyme sucrase, avoiding mixed sugar types in the foods they select (Brugger et al., 1993).
Currently, there are few alternatives to the use of insecticides for the effective control of the corn earworm in sweet corn. The release of biological control agents, such as Trichogramma are typically not effective (Oatman 1966) and are clearly incompatible with current heavy insecticide use patterns. Silk clipping (Carruth 1936) or application of the biological control agent Bacillus thuringensis in combination with mineral oils can be effective but have only been practical on small acreage's. Several types of pest/vegetable crop situations should be amenable to control by fiber barriers, and these include among others: (1) moths which lay their eggs directly on the plant surfaces, (2) maggot adults (flies) which lay their eggs in the soil at the base of the plants, and (3) beetles which feed directly on the newly emerged foliage. Examples of these types of pest/crop situations follow:
The corn earworm is an example of a moth whose egg-laying behavior on plant tissue can be modified through the use of fiber barriers. Because females deposit up to 85% of their eggs directly on the silks of silking corn, it is very difficult to control the larvae, which quickly bore through the silks, and into the ear, where they are protected from most insecticides. Frequent applications of insecticides are required to kill larvae during the 2 to 3 week larval period when ears are most susceptible to damage from this pest. For example, on Long Island, where Lepidopteran (i.e. corn earworm, European corn borer and Fall armyworm) infestations are the most severe in New York State, it is not unusual for growers to make 12 to 14 insecticide applications per planting. This insecticide application is frequently at two to three day intervals during the silking stage of sweet corn development, and reflects an extremely heavy and expensive investment in the use of chemicals.
Similar insecticide use patterns are also common in many other areas, especially in those areas economically dependent upon agricultural production. In Florida, sweet corn fields in silk during peak flights of corn earworm can be treated with 20 or more applications of insecticide over the developmental period of the corn (Mitchell 1978). This heavy insecticide use leads to high ecological and economic costs, and has lead to secondary pest outbreaks of two-spotted spider mites (Pike and Allison 1987). The development of insecticide resistance in target pests is a continuing and growing threat to agriculture around the world (Straub and Emmett 1992). Because of the high use of insecticides in corn and the resulting economic and environmental costs, fiber barriers may be an economically viable alternative to frequent application of insecticides.
Insect pests which lay their eggs at the base of the plant and whose larvae feed on the roots of seedlings are particularly troublesome to growers and usually require prophylactic treatment with synthetic insecticides to the base of the plant or incorporated into the soil at planting to combat crop loss. Such applications are often subject to leaching and are of concern for ground water contamination. The main pest complex, which attacks crop roots, are the various species of maggots. Adult flies are normally attracted to the plant species by visual and chemical cues and lay their eggs at the base of the stem. Larvae develop from the eggs and burrow into the roots. Examples include the cabbage maggot, which feeds on a host of cruciferous crops (broccoli, cabbage, cauliflower, etc.,), the onion maggot, which feeds on onions and closely related crops, and seed corn maggots, which feed on a host of crops including beans and corn. Damage to seeds and roots from these pests may result in death of the plant, diminished yields, or unmarketable roots (i.e. turnips). Because of the similar size and behavior of these maggot pests, it is likely that one type of fiber barrier would be suitable for a host of crop/pest situations and constitutes a large market for the various embodiments of this invention.
Cucumber beetles are the most important direct feeding pests of the cucurbits (cucumber, squash, pumpkin, etc.). These pests are especially difficult for organic growers to control because of their limited options. Colorado potato beetles feed directly on a number of solanaceous crops including tomatoes and potatoes. In both cases, these pests feed on the newly emerged, and very susceptible plants. The goal therefore should be to develop the means, such as non-woven fiber barriers, that are capable of disrupting a given pests ability to find or feed on the leaves or root system of a marketable product (e.g. including the roots themselves). In addition, physical barriers with or without non-toxic pest repellents could provide growers of sweet corn and other crops with substantial gains in overall yield due to a reduction in pest initiated crop destruction or unmarketability.
Few examples of previous efforts with obstructive fiber barriers exist in the literature. Carruth (1936) was one of the few reports in which barriers were tested for control of corn earworm. He compared silk clipping, screen wire protectors, perforated and unperforated bags and insecticides. Most barriers he tested resulted in better control than the insecticides of the day, and none greatly affected pollination. He also studied the use of large enclosures to prevent moth access to sweet corn. Although effective, the barrier treatments were labor intensive and/or expensive to maintain. Likewise, Burbutis and Lesiwicz (1973), found enclosures made of polypropylene netting to be effective in control of European corn borer in sweet pepper. Moreover, pepper yields were found to increase when grown under the enclosures.
Most work with barriers has been directed at disease-vectoring pests (i.e., aphids) using various woven fabric-type materials and reflective mulches or row covers (see references above). For example, Yudin et al., (1991) investigated the effects of barriers on the distribution of thrips in lettuce and Hough-Goldstein (1987) studied the effectiveness of spun polyester as a barrier against seed corn maggot and Lepidopteran pests of cabbage. The latter studies showed a dramatic reduction in worm damage to cabbage under the polyester.